Support arm



FIG. 1 is a perspective view of a support arm showing my new design;

FIG. 2 is a front view thereof;

FIG. 3 is a first side view thereof;

FIG. 4 is a second side view thereof;

FIG. 5 is a top plan view thereof;

FIG. 6 is a bottom plan view thereof; and,

FIG. 7 is a rear view thereof.

The portions of the support arm shown in broken lines form no part of the claimed design. 

CLAIM The ornamental design for a support arm, as shown and described. 